The present invention relates to methods and compositions for removing solubilized organic material from water-like fluids, and more particularly relates, in one embodiment, to methods for removing solubilized organic material from water-like liquid phases using compositions having no or low corrosivity, volatility, or scaling potential.
The production of petroleum hydrocarbons from underground formations usually produces varying amounts of formation or connate water. The production ratio of xe2x80x9cproduced waterxe2x80x9d as it is often called, to petroleum hydrocarbons usually increases over the lifetime of a well. It is not uncommon that oil well production fluids are composed of 90% or more of water and only 10% or less of crude oil. Produced oilfield water contains a diverse mixture of compounds that varies from formation to formation. Of particular importance is the xe2x80x9coil and greasexe2x80x9d (OandG), a conventional pollutant defined in the Clean Water Act and codified at 40 CFR 401.16. OandG comprises those compounds which extract into a non-polar solvent, such as 1,1,2-trichlorotrifluoroethane (Freon 113) or n-Hexane, from water at a pH less than 2 (cf. EPA-600/4-79-020, Methods 413.1 and 413.2). The term xe2x80x9cwater solubilized organicsxe2x80x9d (WSO) has been used to describe a group of these components which are not so extractable when the extract is subsequently treated with silica gel (cf. EPA-821-B-94-004b, Method 1664). These silica adsorbing compounds largely comprise carboxylic acids, which naturally occur in crude oil, whose conjugate bases partition to some significant extent to the produced water at the system pH but which partition to some significant extent as acids to the extraction solvent at the more acidic extraction pH. Thus, under system conditions, they are dissolved, rather than dispersed, in the produced water.
The discharge of WSO has never been desirable. While their concentration may be relatively small, up to 1,000 ppm, they nevertheless give rise to environmental problems when the aqueous phase is discharged into the environment without their removal. These compounds are included in the discharge limits for OandG mandated by Congress in the Clean Water Act. In order to meet those ever more stringent limits, a process to reduce the level of dissolved or xe2x80x9csolubilizedxe2x80x9d organics in the discharged water streams is needed. As discharge limits become more stringent, the need for WSO removal is expected to increase. Furthermore, the water solubilized organics are valuable substances to recover in the produced oil.
One of the first steps after removal of the oil well production fluid is to separate the oil from the water by phase separation techniques. Separation is conventionally accomplished using a bulk separator or a free water knock out system. Virtually all of the hydrocarbon is conveniently recovered in this manner. However, such traditional oil-water separation methods do not remove these WSO compounds from produced water.
Conventional water clarifiers predominantly remove dispersed or xe2x80x9cinsolublexe2x80x9d (not solubilized) oil and generally remove very little, if any, WSO. Cationic polymers might remove the 10-20% of the WSO associated with microemulsions in the produced water, where such emulsions exist.
Over the past several years, many other methods have been utilized to remove WSO from produced water. A variety of filtration and adsorbent media, including ceramics and activated charcoals, reverse osmosis membranes, ion exchange resins, bacterial degradation or other biological treatment, oxidation, distillation, and acidification have all been tried with various degrees of success.
One common, cost-effective method of treatment utilizes mineral acids to lower the pH of the produced water and force the WSO components into the crude oil. Acidification and extraction of the WSO into the crude is simple, cost-effective, and requires very little additional equipment. The mechanism is simple: 1) the more-water-partitioning organic anion salts are converted to the more-oil-partitioning organic acids with protonation by the stronger mineral acid and 2) these more oil partitioning organic acids are extracted into the crude. However, there are significant disadvantages to this method, including, but not limited to, the hazards of handling mineral acid, corrosion problems in storage and processing equipment, scaling of the processing equipment, and reduced effectiveness of conventional water clarifiers.
None of the materials in prior use have proven satisfactory. Hydrohalide and hydrocarboxy acids (HX, H2(CO2)x) are volatile enough to harm human health and downstream distillation processes. Monoprotic oxy acids (HNOx, HClOx) have dangerous oxidation potentials. Nonvolatile, multiprotic oxy acids (HxSOx, HxPOx) are less harmful and less dangerous, but have the additional disadvantage of forming insoluble scale deposits on the production equipment. Nonacidic and cationic compounds have proven unreliable or incompatible with existing water clarifier treatments.
U.S. Pat. No. 5,395,536 discloses a process for removing carboxylic acids from aqueous solutions using a composition of a polyaluminum chlorohydrate and a cationic polyelectrolyte. After or during the initial contact of the aqueous solution with the composition, an organic liquid may optionally be added after which separation into an aqueous phase and an organic phase occurs whereby the organic acids are removed in the organic phases. The preferred polyaluminum chlorohydrate is aluminum chlorohydrate, and the preferred cationic polyelectrolyte is a high molecular weight poly(dimethyl diallyl) ammonium chloride.
Another method for removing organics, such as water soluble organics (WSO) from fluids containing water, such as oil process water is described in U.S. Pat. No. 6,159,379 that involves contacting the fluid with an effective amount of an organic ammonium salt. No added acid is necessary, although in some embodiments, weak acids such as glycolic acid, can be used to give synergistic improvement in organic removal. Suitable organic ammonium salts have the formula: R1R2R3N+H Xxe2x88x92, where R1 is a saturated or unsaturated alkyl group or an aryl group, or saturated or unsaturated alkyl group or an aryl group substituted with a heteroatom selected from the group consisting of N, O, S, P and halogen; R2 and R3 are independently H or a saturated or unsaturated alkyl group or an aryl group, or saturated or unsaturated alkyl group or an aryl group substituted with a heteroatom selected from the group consisting of N, O, S, P and halogen; and X is a halogen atom or an anion of a protic acid.
It would be desirable if a simple, economical procedure for removing WSO compounds from water without the disadvantages of using strongly acidic materials could be devised.
Accordingly, it is an object of the present invention to provide a composition and method for removing WSO from produced water that does not require the use of strong acids.
It is another object of the present invention to provide a method and composition for removing WSO from produced water that does not create scaling problems and that is compatible with conventional water clarifier treatments.
In carrying out these and other objects of the invention, there is provided, in one form, a method for removing water solubilized organics (WSO) from a water-like fluid phase involving contacting the water-like fluid phase with an effective amount of a hydrophilic xcex1-hydroxymonocarboxylic acid (AHA) and separating at least one WSO from the water.